I’m in US zone 7b so we usually get a winter with snow and sub freezing temperatures December-March. Both aphids and ladybugs will die off during winter but leave eggs that remain and hatch in the spring. Each year I supplement the natural occurring ladybugs and usually release approximately 3000 when the aphids appear. That sounds like a lot but it’s only two small containers. I rely on the ladybugs for pest control and never use insecticides as I want a natural ecosystem to flourish. Most years it works out and my garden remains healthy. Right now the aphids are ravishing my beets and poppies. Fingers crossed the ladybugs will triumph and reign in the aphids before I lose too many plants. Soon these ladybugs will lay eggs (during summer) and the resulting larva will do most of the work. The larva look like small six legged alligators and you can observe them picking up aphids and eating them. It’s fascinating to watch.